package com.quickask.operate.encode;

import java.util.BitSet;
import java.util.HashMap;

/**
 * Created by hackway on
 * Date: 2015/11/4.
 * Time:10:26
 */
public class Geohash {

    private static int numbits = 6*5;
    final static char[] digits =  { '0', '1', '2', '3', '4', '5', '6', '7', '8',
            '9', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k', 'm', 'n', 'p', 'q',
            'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z' };
    final static HashMap<Character, Integer> lookup = new HashMap<Character, Integer>();

    static {
        int i=0;
        for(char c:digits) {
            lookup.put(c,i++);
        }
    }

    //解码
    public double[] decode(String geohash) {
        StringBuilder builder = new StringBuilder();
        for(char c:geohash.toCharArray()) {
            int i= lookup.get(c)+32;
            builder.append(Integer.toString(i, 2).substring(1));
        }
        BitSet lonset = new BitSet();
        BitSet latset = new BitSet();

        //even bits
        int j=0;
        for(int i=0;i<numbits*2;i+=2) {
            boolean isSet = false;
            if(i<builder.length()) {
                isSet = builder.charAt(i) == '1';
            }
            lonset.set(j++,isSet);
        }

        //odd bits
        j = 0;
        for(int i=1;i<numbits*2;i+=2) {
            boolean isSet = false;
            if(i<builder.length()) {
                isSet = builder.charAt(i) == '1';
            }
            latset.set(j++,isSet);
        }

        double lon = decode(lonset,-180,180);
        double lat = decode(latset,-90,90);
        return new double[]{lat,lon};
    }

    private double decode(BitSet bs, double floor, double ceiling) {
        double mid = 0;
        for(int i=0;i<bs.length();i++) {
            mid = (floor+ceiling)/2;
            if(bs.get(i))
                floor = mid;
            else
                ceiling = mid;
        }
        return mid;
    }

    //编码
    public String encode(double lat, double lon) {
        BitSet latbits = getBits(lat,-90,90);
        BitSet lonbits = getBits(lon,-180,180);
        StringBuilder buffer = new StringBuilder();
        for(int i=0;i<numbits;i++) {
            buffer.append(lonbits.get(i)?'1':'0');
            buffer.append(latbits.get(i)?'1':'0');
        }
        return base32(Long.parseLong(buffer.toString(),2));
    }

    /**
     * 经纬度分区
     * @param lat
     * @param floor 下界
     * @param ceiling 上界
     * @return
     */
    private BitSet getBits(double lat, double floor, double ceiling) {
        BitSet buffer = new BitSet(numbits);
        for(int i=0;i<numbits;i++) {
            double mid = (floor+ceiling)/2;
            if(lat>=mid) {
                buffer.set(i);
                floor = mid;
            } else {
                ceiling = mid;
            }
        }
        return buffer;
    }

    //base32编码
    public static String base32(long i) {
        char[] buf = new char[65];
        int charPos = 64;
        boolean negative = (i<0);
        if(!negative)
            i=-i;
        while (i<=-32) {
            buf[charPos--] = digits[(int)(-(i%32))];
            i/=32;
        }
        buf[charPos] = digits[(int)(-i)];
        if (negative)
            buf[--charPos] = '-';
        return new String(buf,charPos,(65-charPos));
    }

}
